My Favourite Coevolutionary Relationship!

I have saved this relationship for now because it is one of my favourites!!

Has anyone wondered how crustaceans can sometimes remain hidden from sharks even though the sharks have the electrosensory ability to detect the electrical pulses made by the heart when it beats?? Well I wondered, so I did some research and found out some incredible things.

Firstly, it is due to coevolution. Secondly, it is due to the crustaceans’ ability to induce cardiac arrest when they feel threatened!!! For example, when a shadow passes overhead that could be a potential predator. This absolutely blew my mind when I heard about it. 

In this case it is predator-prey coevolution; the reason why it is coevolutionary is due to the sharks initially gaining an upper-hand with electrosensory detection, due to an electric signal produced each time the heart pulses; the crustaceans followed by allowing their heart to stop until a threat has past, therefore having the ability to hide from the sharks' electro-sensors (Burnovicz et al., 2009).

Neil Gribble, lecturer at JCU Cairns, did his PhD thesis on this topic, finding that crustaceans still retained the ability to see and catch potential prey even if their heart was “stopped”. There must have been a way for it to retain enough blood circulating to its eyes and brain in order to respond like this. He found that there is a tiny muscle just above the heart that contracts in a very subtle and even way so that enough blood is circulated to the eyes and brain to remain alert, but not enough to emit an electrical signal to other predators.

References:

Burnovicz, A., Hermitte, G., Oliva, D. 2009. The cardiac response of the crab Chasmagnathus granulatus as an index of sensory perception. Journal of Experimental Biology, 212, 313-324.

Image of crab sourced 14/5/14: http://marinebio.org/gallery/indonesia/

Image of shark sourced 14/5/14: http://www.xray-mag.com/Batoidea?page=3

Obligate Mutualism in Coevolution

For my blog this week the focus will be on a coevolutionary relationship that could date back to the Eocene epoch, 40 million years ago! It is also a major model system for the study of coevolving species interactions.

The yucca moth and yucca plant share an obligate mutualistic relationship, meaning that both organisms depend entirely on each other for survival. Yucca moths provide an important pollination service to the plant. In return, as well as providing a meal in seeds for the moth larvae, the plant allows with moth to lay its eggs in a deep place within the flower so that they are protected from predators (Pellmyr & Leebens-Mack, 1999).

Before a female moth lays her eggs she collects pollen from a flower; to do this she must scrape pollen from the anthers of the flower with specialised mouth parts and packs it into a ball, securing it under her head. After that she flies to another flower and climbs to the deepest part of the flower, opens a hole in the ovary and lays her eggs inside the ovary of the flower. She then climbs to the flowers’ stigma, retrieves the ball of pollen that she collected earlier and packs it into the tiny depressions that are within the style. Interestingly, before she moves on to a different flower, she marks it with a pheromone to notify any other moths that she has already laid her eggs here. This is done because if too many eggs are laid in the flower, the plant itself will abort the flower.

Both organisms show coadapted traits; mediated pollinator specificity due to structural adaptations in the flower; and specific behaviours for collection and deposition of pollen in the moth.

References:

Pellmyr, O., Leebens-Mack, J. 1999. Forty million years of mutualism: Evidence for Eocene origin of the yucca-yucca moth association. Proc. Natl. Acad. Sci. USA, 96(16), 9178-1983.

Image sourced 5/5/14: http://www.bobklips.com/earlyjuly2008.html